he human B cell cycle was analyzed with regard to the distinct hases of activation, proliferation, and differentiation. esting B cells were isolated and driven through the cell cycle y a sequential series of signals. The distinct roles of the pectrum of growth and differentiation factors for human B ells were precisely delineated. These factors which were erived from human T--T cell hybridomas as well as cloned T ell lines were purified and characterized in preparation for mino acid sequencing and ultimate cloning of genes for their xpression. For the first time in the human system, a ransformed B cell line was identified which produced a B cell rowth factor (BCGF). Production of BCGF by B cell tumor lines ay contribute to their ability to grow autonomously and may eflect an important component of the neoplastic potential of B ells as well as the normal autoutilization of factors. IL-2 eceptors were identified on normal activated human B cells hich suggests a role for this factor in normal B cell unction. The immunoregulation of antigen-specific human B ell responses was studied including the role of various Ia ositive cells in antigen presentation and the effect of in itro IL-2 on antigen-specific T cell clones on human B cell unction. The first in vitro system for the study of specific ntibody production to hepatitis B surface antigen was eveloped. The pharmacologic modulation of the distinct phases f the human B cell cycle was studied, and it was demonstrated hat corticosteroids and cyclosporin A exhibited selective uppressive effects on the early events of B cell activation ith relatively little effects on proliferation and ifferentiation. Finally, the selective effects of yclophosphamide on certain distinct phases of the human B cell ycle were demonstrated.